The present invention relates generally to a mobile grain harvesting and threshing machine and, more particularly, to an axial flow combine in which there is provided an improved grain receiving area for collecting threshed and separated grain without the disruptive effect of air currents generated by the operational rotary components.
The instant invention is generally incorporated in an axial flow type combine having longitudinally extending threshing and separating means. The threshing and separating means are in the form of a pair of side-by-side rotors with distinct threshing and separating sections. This type of axial flow combine is fully described and shown in U.S. Pat. No. 3,669,122 to E. W. Rowland-Hill, issued June 13, 1972. This invention is particularly adaptable to the type of combine disclosed in U.S. Pat. No. 4,078,571 to Todd et al, issued Mar. 14, 1978, wherein a shortened threshing and separating rotor is used in a generally cylindrical crop handling unit employing 360.degree. or continuous separation. The continuous separating feature makes possible the use of a shortened rotor without affecting overall machine capacity. Although the present invention will be described in the context of a harvesting and threshing machine employing two side-by-side rotors, it should be noted that the principles disclosed hereafter are equally applicable to a combine employing any number of axially extending centrifugal threshing and separating means.
U.S. Pat. No. 3,669,122 is specifically directed to an axial flow type combine utilizing a rear discharge beater assembly that redirects the flow of crop material as it exits the threshing and separating cylinders prior to the material's discharge from the combine. This redirection of the crop material by the rotary beater discharge provides an auxiliary separation function to separate any grain which may still be entwined within the crop material. The grain is separated by being passed through a generally concave grate beneath the rotary discharge beater so that it falls onto a grain collection pan. The rotary discharge beater concurrently propels the waste or chaffy crop material rearwardly thereby discharging it from the combine. This direct expulsion of the waste crop material into the rear of the machine permits it to be processed in diverse ways, such as chopping, spreading or laying the crop material in a windrow behind the combine on the field. However, it has been discovered during the operation of axial flow type combines employing this type of rotary discharge beater and grate assembly that air flow generated by the beater assembly interferes with the air flow generated by the blower or fan of the cleaning means. This creates undesirable and disruptive air currents above the cleaning sieves. Such disruptive air currents disturb the pneumatic grain separation across the cleaning sieves and frequently results in the grain being blown or mechanically discharged by the counter-reciprocating motion of the cleaning assembly out the rear of the combine. Such grain loss also can be created by the rotation of the longitudinally extending threshing and separating rotors. These rotors produce an air current that passes through the separation grates and compound the problem of grain loss. This disruptive effect of the air passing through the various grates is particularly evident at the slow fan speeds of the cleaning system which must be maintained when operating in light kernel crops.
U.S. Pat. No. 3,916,912 to Rowland-Hill, issued Nov. 4, 1975, addresses this problem by replacing the separation grate beneath the rotary discharge beater with an impervious plate member which prevents the air flow from passing into the cleaning sieve area and thereby increasing the grain loss by blowing the grain from the sieves out the discharge opening at the rear of the machine. However, this solution forfeits the benefit of having the potential for auxiliary separation obtained by employing a rotary discharge beater. To fully exploit this feature an open type grate must be provided radially for a distance about the beater.
Other approaches have been taken to prevent the interference of this secondary air flow from the rotors and beater discharge assembly with the operation of the combine harvester cleaning sieve area. One such approach is shown in U.S. Pat. No. 3,847,160 to Decoene et al, issued Nov. 12, 1974. This patent discloses a combined collection grain pan and protective screen that is suspended beneath the rotors, as well as the discharge beater assembly and its auxiliary separation grate, but above the primary grain pan to prevent this secondary air flow from interfering with the grain cleaning operation. This structural arrangement deflected the secondary air flow from the rotors and the beater discharge assembly forwardly so that a precleaning of the grain was effected. The chaff or waste material carried forward in the deflected air flow was discharged out a forward chaff outlet. The obvious drawback to this type of a system is that it requires additional space within the combine and entails the additional cost of installing the collector pan and protective screen beneath the rotary components. This additional structure also adds greater weight to the components and to the reciprocating mechanisms in the cleaning area. This additional weight tends to increase the stress on the reciprocating parts and, therefore, increases the chance for failure. Lastly, this structure increases the chance of plugging or clogging of the grain pan under moist conditions since the dust that naturally builds up in such an area has the tendency to turn to mud under such conditions and can clog the grain pan and impede the natural flow of material. Since the structure shown in the Decoene patent requires the grain to travel a greater distance along the grain pans by moving first forwardly on the collector pan and protective screen and then rearwardly on the main grain pan prior to reaching the cleaning and chaffing sieves, there is a greater opportunity for plugging to occur when combines are operated under conditions with high moisture.
Additionally, in combines of the type discussed above, there is the possibility that crop material, such as corn cobs, could be passed through the beater discharge assembly grate at high velocity and impact upon the relatively fragile sieve bills of the grain and chaffer sieves. Such impacting causes damage to the sieves which is both costly and time consuming to repair. Since time is of the essence during the harvesting season, such damage can be especially significant if harvesting must be interrupted to repair it. If time is so critical that the harvesting cannot be interrupted to repair the sieves, the combine harvester will operate at reduced efficiency and higher grain losses.